Dr Matthew Lam discusses the truth behind new reports that eating close to bedtime could raise the risk of breast cancer.

You may have seen today several news outlets reporting that “eating close to bedtime could raise the risk of breast cancer” or “fasting at night lowers risk of breast cancer and diabetes”.  These headlines, and the articles themselves, are misleading and not a fair representation of the research being discussed.

We have to start off by saying, again, that the journalists can’t be held fully responsible for this story. The original press release did no favours by sending out the wrong message. 

The press release begins with the statement: “Eating regular meals at set times and then waiting longer between the last meal of the day and breakfast reduced glucose levels and breast cancer risk.”

So you can see where the media picked up its message.  So what really should have been reported?

Blood glucose, not breast cancer

In this study the researchers analysed a range of dietary and lifestyle information collected from study participants.  The data they were most interested in was the length of time between a person’s last meal of the day and breakfast, and their blood glucose level two hours after eating.  In short, they found that for each additional three-hour period a person didn’t eat between dinner and breakfast, there was a 4% lower blood glucose level when taken two hours after a meal.  So it seems that if you don’t snack throughout the night but wait until breakfast then you appear to be better at regulating blood glucose.

This is great - a nice short study investigating the impact of one action on another (there are all the usual caveats here regarding studies of this type). What you may have noticed is that there hasn’t yet been any mention of breast cancer.  That’s because this study doesn’t even look at the effects of late night snacking and breast cancer risk. No one in the study was assessed to see if they went on to develop breast cancer so no conclusions can be drawn about the effects of snacking at night.

But why?

The reason this speculation was made is because women with type 2 diabetes have an increased risk of breast cancer, and poor regulation of blood glucose levels is a contributing factor to diabetes.  The reasoning makes sense, and could be true, but we can’t come close to being sure from this study. 

It’s a shame that the authors, the journal and the press office felt that they had to sell the study to the media in this way.

Katie Goates in our Research Communications team summed it up nicely:

As the researchers did not assess the breast cancer risk of the women taking part in this study the claim that the length of time fasting overnight could affect a person’s breast cancer risk is unfounded. The researchers also highlight that no other studies have proven a link between longer periods of night-time fasting, its resulting influence on the body’s glucose uptake and breast cancer risk.

Not snacking at night may improve your blood glucose regulation

In conclusion, this study doesn’t show in any way that late night snacking increases breast cancer risk.  What it does show is that not snacking at night may improve your blood glucose regulation, but that is all.

Dr Matthew Lam is a Senior Research Communications Officer